The present invention relates to the field of electrical filters, and in particular, a resonator that can be used in combline filters operating at microwave frequencies.
In modern electrical and electronics systems environments, particularly in advanced multi-signal radio frequency (RF) system architectures, system components are subject to the demands of varying frequency ranges, to smaller and smaller physical size and configuration restraints, and to lower weight and lower cost requirements.
Well-known to those skilled in the art is the combline filter which employs one or more resonators. The combline filter is an important component of such advanced multifunction RF system architectures and such modern systems' environments. Of particular concern is the ability to have smaller filters for a given frequency. Smaller filters are attractive for many system requirements that include smaller height, lower cost, lower weight.
Typically, one or more cylindrical posts are used in a rectangular housing to form a combline filter. The length of the post and the distance from the opposing wall are adjusted until resonance at the desired frequency is achieved.
Various prior art approaches have been employed to lower the resonating frequencies and to minimize size. One approach to make the typical resonator resonate at lower frequencies is to decrease the gap between the post and the opposing wall. However, as the gap becomes smaller, the sensitivity of the resonant frequency is significantly and nonlinearly increased. An approach for reducing the size usually includes the introduction of other materials to reduce the electrical wavelength within the filter. However, these added materials usually increase the propagation losses for the entire filter.
Therefore, a need exists for an efficient combline resonator and filter capable of operating at reduced frequencies with minimal propagation loss, while maintaining a small size. The present invention provides a solution to meet such needs.